The closest thing to a fake I I have come across is a seller selling exact copies of MAM's in leather, but they dont use the RM name on it...I dont think. They do have a few pics of celebs carrying real RM's though so they are true copies of the bag. The seller also sells copies of other designer bags too.
I have a pic of one of their copies below but I shaded out the sellers name as I dont want to advertise them.